9 ms·

Quantum Mechanics for Programmers

240 points by taheris 10y ago

nivwusquorum 10y ago
I actually find those notes particularly well suited for programmers: http://www.cl.cam.ac.uk/teaching/1516/QuantComp/materials.html http://www.cl.cam.ac.uk/teaching/1516/QuantComp/materials.ht...
eastWestMath 10y ago
Why not categorical quantum mechanics?
- jesuslop 10y ago
  Yeah I'm reading a nice book from Coecke and Kissinger [1] just issued and am loving it, it's the story of String Diagrams for a wider audience and with all the details fleshed out (not just hinted as in Baez TWFs). Monoidal categories, tensor networks, directed PGMs, quantum computing and even vector space NLP semantics are all particulars seen from this vantage point. [1] Picturing Quantum Processes, ISBN 1108107710
  - credit_guy 10y ago
    This book looks very promising. I just bought the kindle version on amazon. Thank you.
monktastic1 10y ago
Hmm he seems to imply that MWI is the "right" interpretation, and that the measurement problem is solved. Most physicists would not agree. If you follow the link to his MWI description, there's this gem: > But fortunately, I knew computer science, which most physicists do not know, with the Church-Turing thesis, which roughly states that anything physical can be simulated by a computer. But that is not what the Church-Turing thesis says. A Turing machine cannot mimic a truly random physical process, pretty much by definition. And then: > This means that observers can be simulated by a computer. Except that nobody really understands what kinds of physical interactions qualify as measurements -- or even if that is the right framework to use at all.
- platz 10y ago
  I thought "coherence" was the model by which quantum systems spread entanglement to other systems; the larger the system the 1st system into contact with, the bigger the effect of coherence loss in the 1st system and the larger the "measurement"
  - monktastic1 10y ago
    It is generally agreed (except, perhaps, by the strongest champions of the decoherence program) that decoherence does not completely solve the measurement problem. Some good references here: http://physics.stackexchange.com/questions/295527/decoherence-does-it-solve-the-measurement-problem-is-it-discontinuous-when-do http://physics.stackexchange.com/questions/295527/decoherenc... It helps explain the loss of interference, but it does not resolve the question of why and how we see one particular outcome.
    - platz 10y ago
      > it does not resolve the question of why and how we see one particular outcome. agreed. dechoherence doesn't explain particular outcomes. It explains the scale & magnitude of mixing quantum states from different systems. I thought "what kinds of physical interactions qualify as measurements" was referring to a different part of understanding QM. Decoherence doesn't explain which outcome, it does explains "part" of (or place constraints upon) the mechanism of measurement process.
      - adrianratnapala 10y ago
        The problem here is that very much of what we mean by "scale and mangitude" boils down to the frequency of particular outcomes when situations are repeated. So Decoherence only explains those things after you already have the Born rule (P ∝ |Ψ|^2). But that's the very thing we are trying to explain!
        platz 10y ago
JadeNB 10y ago
This seems just to be a model of systems evolving according to discrete difference equations, admittedly derived from quantum mechanics; it doesn't seem to have much to say about quantum mechanics per se. It reminds me of a lower-(math-)tech version of SICM (https://mitpress.mit.edu/sites/default/files/titles/content/sicm/book.html https://mitpress.mit.edu/sites/default/files/titles/content/...).
aphextron 10y ago
The more I learn about physics and math, especially with regards to quantum theory, I start to get really freaked out. The amount of "neatness" to the universe is staggering. How there's no "inbetween" at the smallest scales. Everything is discrete. The fact that simple arrangements of symbols on a screen can perfectly describe this behavior is mind blowing. It leads me to think there's no possible way we're not living in some type of computer simulation.
- platz 10y ago
  > It leads me to think there's no possible way we're not living in some type of computer simulation. I find this line of reasoning inadequate. In the 19th century, would you not be compelled to believe that the universe was made of mechanical pulleys, levers, and pipes because the universe operated with the perfection of a well-designed machine? OK, so there are some phenomena that correlate (bear a resemblance to) with how computers behave. well, there are phenomena that correlate with a great many number of things; we shouldn't be surprised that computers and information theory are one of them
- krastanov 10y ago
  Minor nitpick: We definitely do not know whether everything is discrete. There are plenty of quantum mechanical phenomena that do not have discrete spectra (you can have light of any wavelength for instance (with some caveats at the extremes of the energy scales)). We also do not have theoretical or experimental proof that space-time is discrete at the Plank length-scale - all we know is that our current theories break at that scale. See https://physics.stackexchange.com/questions/9720/does-the-planck-scale-imply-that-spacetime-is-discrete https://physics.stackexchange.com/questions/9720/does-the-pl... (the given answer is pretty great, but beware, the author is known for being a bit hostile in his non-physics opinions)
  - eutectic 10y ago
    Luboš is known for being extremely hostile in all his opinions. :)
  - aphextron 10y ago
ycmbntrthrwaway 10y ago
> Here is a model of waves, as in light or sound, but not as in water waves or electron waves How water waves are different from sound? Water wave are sound, aren't they?
- ajkjk 10y ago
  Well, water waves can either be surface waves or pressure waves. The latter is the same mechanism as sound.
- btilly 10y ago
  The wave that he is modeling is due to having a field in space-time that will interact with nearby values of the same field in a linear way, which results in it moving at a constant rate. The waves that you see in water are the surface representation of 3-d movements under the surface of the water. So you get effects such as the depth of the movement for a wave determines its velocity. A wave that moves a very deep water column moves very fast. (One that is a half-mile deep can move as fast as a jet!) A wave that moves a shallow water column moves slowly. Another interesting fact about waves is that there is a significant nonlinear interaction between the depth of the water and the depth of the wave. As you come to shore this causes the wave to rise up. Surfers enjoy this effect when it comes to normal wind driven waves. But in the case of very deep and fast waves, the effect is very much like a tide unexpectedly coming in. The result is known as a tsunami or tidal wave. These complex behaviors mean that water waves can behave very differently from light and sound.
d_burfoot 10y ago
> Since you are a programmer, you do not know what science is, even though you may believe you do. A hint: Computer science does not contain science, just mathematics. He probably wrote this half in jest, but it is actually a serious issue in fields like Natural Language Processing and Computer Vision that are have their intellectual roots in Computer Science. Papers in CV and NLP are about data structures, algorithms, software engineering methods, neural networks, statistical models, and so on. They do not discuss anything in particular about the structure of language or the properties of images. This is because they are descended from CS. In CS, exemplar results are ideas like QuickSort and Dijkstra's algorithm. These algorithms work on any list or graph; you do not have to know anything special about the particular properties of the list or graph you are operating on. As an illustrative anecdote, I went to an NLP talk given at MIT by a well-known Google/Berkeley parsing researcher. He gave a talk about a system that used neural networks to do sentence parsing. In the QA session, I mentioned the idea of verb argument structure, and asked how the system would learn, for example, that a verb like "persuade" or "argue" can take a that-complement, while other verbs cannot. He didn't really have an answer, because it wasn't the kind of thing that he worried or thought about. My guess is that he did not consider such a question to be relevant to his field.
- deleted 10y ago
  [deleted]
- neshibble 10y ago
  I do research on Deep Learning. That seems the exact kind of question they would deem relevant to their field. I don't know much about NLP but if I had to guess the answer to your question is include it in the training data. I don't know what model they use, but presumably it parses out sentence structure in a specific format and uses that as input to some neural network architecture. Not really sure why he didn't answer your question, it's the exact kind of question people do NLP to answer.
Coding_Cat 10y ago
Hey, something I can comment on properly for once ;). Handed in my final Quantum-field-theory homework yesterday (or blood-sweat-and-theory as I called it, great fun) and finishing a MSc. in Computational science 'soon'. From what I can follow, most of it is, unfortunately either varying degrees of wrong or just confusing as all hell. :\ Some assorted quotes: >The electron is not in a single place, but instead spread out over all the positions, more or less. This is called "superposition". No, the superposition principal states that individual states (contributions) can be summed in a linear fashion. I know this is not a very clear way of wording it, but it is one of those things I think is quite hard to word but very easy to understand once you see it. (Although one could say this is a form of superposition, namely a sum of infinite delta functions in position-space. But this would be the most confusing example to use) >The smart programmer would guess at a model containing more complex math that will get the array to model several particles, but no such thing exists. Quantum field theory. > These examples have used cubes with a width of 1000 voxels, and of 1000 time instants. The Universe use a width of something like 10^70 voxels. The same goes for time. I assume this is (roughly matches) size-of-observable-universe/plank-length. But this is misinterpretation of the planck length. As far as we (I) know, spacetime is continouis. (string theorist migth disagree, I am not familiar). Furthermore, the many particle approach is not at all reasonable. One would (usually) use lattice-QFT. where one simulates a field for each type of particle (the field can have several components) and particles are identified as excitation of this field. The most well known is lattice-QCD. >Quantum Electro Dynamics Quantum Electrodynamics ;) >Richard Feynman got the nobel prize for figuring out a way of doing this. His Quantum Electro Dynamics is a sort of dynamic programming method This part is right (I have no idea what the next few sentences are trying to say). Feyman diagrams (those fun squilly drawings) represent the results of some awful, awful integrals. The real analytical answer is integrated over two infinite spaces. But one can do a taylor expansion to get a answer which can be computed. Feynman noted that you can read off a few rules from this approximation and assign drawings to them. The answer can then be computed by summing all (topologically distsinct graphs) instead of the terms in the Taylor sum. It's much easier than it sounds (and sure as hell more fun than doing integrals), and you can copy-paste entire sections of your diagrams as long as the in and out-puts match up. perfctly suitable for dynamic programming.
halfnibble 10y ago
I feel like this is what's wrong with the world: "In science one guesses at explanations. One does not deduce them like one do in math." As a programmer who took quantum mechanics in college, I have to admit, I didn't understand most of it. Someone I respect once told me that if you think you understand quantum mechanics, then you don't understand any of it at all. The mathematical portion, vector mathematics with imaginary numbers, was the only part that was interesting to me. It seemed to me that mathematical deductions were necessary because the phenomenon modeled nothing in our "reality."
madhadron 10y ago
This puzzles me extremely. There are very insightful statements like > One does not deduce them like one do in math. The physicists who actually did this stuff apparently knew this, and considered the math more akin to toying with the models to see what happens, to see if they could get better models Which is absolutely true. Part of the problem with quantum mechanics texts is that they're almost all descended from Oppenheimer's lectures (via Schiff's book) to graduate students who already knew this, and just needed someone to brain dump the latest techniques. But then it's mixed with really basic misunderstandings, like > Many physicists like to believe that this makes the underlying model irrelevant; that the matrix behaviour, its eigenvalues, is the only thing that matter. You will encounter lots of this in books about Quantum Mechanics. This however is not science, because it ignores Ockhams Razor; the models shall be the simplest ones. A sparse matrix is simpler than when it is Fourier transformed, or put into atom orbitals. (I thank Eliezer Yudkowski who gave a reminder that Ockhams razor belongs here too.) Quoting Eliezer Yudkowski is a useful heuristic for not taking someone seriously, but this quote implies that the author missed the whole point of linear algebra. And is falling into the traps described by Theorem IV in van Kampen's [Ten Theorems about Quantum Mechanical Measurements](http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=617AE275E5CECF5F0AFD69ACBC52141B?doi=10.1.1.205.6529&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=617...).
partycoder 10y ago
You can also read the Feynman lectures on computation, has some notes on quantum computing.
B1tchard0 10y ago
This article could have been written by an algorithm. Everyone knows the meme about Quantum Mechanics being incomprehensible, like, ~"if you understand quantum mechanics, you don't understand quantum mechanics". Quantum Mechanics requires randomness, because determinism is scary. Both probability and fate are functions of time, and time is the most interesting thing to look at. Generally, Time is ignored, or at best "accounted for". As a programmer I think time is more interesting than particles or fields or probabilities of wave-function whatever
- AgentME 10y ago
  >Quantum Mechanics requires randomness, because determinism is scary. Isn't the many-worlds interpretation generally regarded as deterministic?
  - n4r9 10y ago
    Yes, as is de-Broglie-Bohm interpretation. Some others make no assertions about determinism. I interpreted "because determinism is scary" as a tongue-in-cheek aside. Either way, time is not ignored: there is serious research effort into the concept of time in quantum mechanics.
  - naasking 10y ago
    IIRC, it's deterministic in a sense that isn't equivalent to the way de Broglie-Bohm is deterministic. The latter is generally what people mean by deterministic, ie. it's a classical theory with an extra term to account for quantum influences.
    - n4r9 10y ago
      Both theories model the universe as being in a definite, non-probabilistic state, and that the state at one time determines the state at all future times. But yeah there is some difference in the anthropocentric aspects, i.e. how our observation of probabilities actually arises.
hota_mazi 10y ago
It's puzzling to see the author call himself multiple times a scientist while lending so much importance to Occam's razor (which is spelled differently in the article, not sure if it's an alternative spelling in his language or a mistake). Occam's razor is not a law. It's not a fact. It's a simple suggestion if you're looking for a starting hypothesis. Not sure which way to start to investigate a phenomenon? Pick the simplest one and verify that one. It doesn't mean it's right, it doesn't mean it's wrong, just that it's a reasonable first guess. But not a proof. Not a fact. Just a guess that's statically more likely to be right.
- defined 10y ago
  Occam is the Latinized version of Ockham, as in "William of Ockham" [1]. [1]: https://en.m.wikipedia.org/wiki/William_of_Ockham https://en.m.wikipedia.org/wiki/William_of_Ockham
  - TheOtherHobbes 10y ago
    Which must be the correct spelling, because it's shorter.
  - deleted 10y ago
    [deleted]
- stan_rogers 10y ago
  Ockham is arguably the proper spelling when the name isn't being rendered in Latin; Ockham is where William was from.
- dragonwriter 10y ago
  > It's a simple suggestion if you're looking for a starting hypothesis. While it can be used to select priority for exploring hypotheses, it's at least as valuable as a method of choosing from among models with equal explanatory power once they've been tested and established to have equal explanatory power.
- sideshowb 10y ago
  Ock/cham's razor is a heuristic, not a law. It also runs into weirdness combined with MWI. Are infinite universes the simplest explanation, or have you just literally broken Occam's razor in the most egregious way possible?
yorwba 10y ago
There is lots of undefined behavior in the code examples, where x-1 is used as an index although x starts from 0. I guess he didn't want to talk about boundary conditions?
sideshowb 10y ago
A slightly wacky article, but I do think there is lots more scope for explaining quantum physics via programming concepts. I got what little understanding I have of QM by creating a game that simulates it. I even made my own wacky article as well :) https://linkingideasblog.wordpress.com/2016/04/25/learning-quantum-mechanics-the-easy-way/ https://linkingideasblog.wordpress.com/2016/04/25/learning-q...
andrepd 10y ago
This article does not elucidate anything about Quantum Mechanics, is quite confusing, and indeed is plain wrong in several aspects. Very disappointing.

240 points by taheris 10y ago

I actually find those notes particularly well suited for programmers: http://www.cl.cam.ac.uk/teaching/1516/QuantComp/materials.html http://www.cl.cam.ac.uk/teaching/1516/QuantComp/materials.ht...

eastWestMath 10y ago

Why not categorical quantum mechanics?

jesuslop 10y ago
Yeah I'm reading a nice book from Coecke and Kissinger [1] just issued and am loving it, it's the story of String Diagrams for a wider audience and with all the details fleshed out (not just hinted as in Baez TWFs). Monoidal categories, tensor networks, directed PGMs, quantum computing and even vector space NLP semantics are all particulars seen from this vantage point. [1] Picturing Quantum Processes, ISBN 1108107710
- credit_guy 10y ago
  This book looks very promising. I just bought the kindle version on amazon. Thank you.

monktastic1 10y ago

Hmm he seems to imply that MWI is the "right" interpretation, and that the measurement problem is solved. Most physicists would not agree. If you follow the link to his MWI description, there's this gem: > But fortunately, I knew computer science, which most physicists do not know, with the Church-Turing thesis, which roughly states that anything physical can be simulated by a computer. But that is not what the Church-Turing thesis says. A Turing machine cannot mimic a truly random physical process, pretty much by definition. And then: > This means that observers can be simulated by a computer. Except that nobody really understands what kinds of physical interactions qualify as measurements -- or even if that is the right framework to use at all.

platz 10y ago
I thought "coherence" was the model by which quantum systems spread entanglement to other systems; the larger the system the 1st system into contact with, the bigger the effect of coherence loss in the 1st system and the larger the "measurement"
- monktastic1 10y ago
  It is generally agreed (except, perhaps, by the strongest champions of the decoherence program) that decoherence does not completely solve the measurement problem. Some good references here: http://physics.stackexchange.com/questions/295527/decoherence-does-it-solve-the-measurement-problem-is-it-discontinuous-when-do http://physics.stackexchange.com/questions/295527/decoherenc... It helps explain the loss of interference, but it does not resolve the question of why and how we see one particular outcome.
  - platz 10y ago
    > it does not resolve the question of why and how we see one particular outcome. agreed. dechoherence doesn't explain particular outcomes. It explains the scale & magnitude of mixing quantum states from different systems. I thought "what kinds of physical interactions qualify as measurements" was referring to a different part of understanding QM. Decoherence doesn't explain which outcome, it does explains "part" of (or place constraints upon) the mechanism of measurement process.
    - adrianratnapala 10y ago
      The problem here is that very much of what we mean by "scale and mangitude" boils down to the frequency of particular outcomes when situations are repeated. So Decoherence only explains those things after you already have the Born rule (P ∝ |Ψ|^2). But that's the very thing we are trying to explain!
      - platz 10y ago

JadeNB 10y ago

This seems just to be a model of systems evolving according to discrete difference equations, admittedly derived from quantum mechanics; it doesn't seem to have much to say about quantum mechanics per se. It reminds me of a lower-(math-)tech version of SICM (https://mitpress.mit.edu/sites/default/files/titles/content/sicm/book.html https://mitpress.mit.edu/sites/default/files/titles/content/...).

aphextron 10y ago

The more I learn about physics and math, especially with regards to quantum theory, I start to get really freaked out. The amount of "neatness" to the universe is staggering. How there's no "inbetween" at the smallest scales. Everything is discrete. The fact that simple arrangements of symbols on a screen can perfectly describe this behavior is mind blowing. It leads me to think there's no possible way we're not living in some type of computer simulation.

platz 10y ago
> It leads me to think there's no possible way we're not living in some type of computer simulation. I find this line of reasoning inadequate. In the 19th century, would you not be compelled to believe that the universe was made of mechanical pulleys, levers, and pipes because the universe operated with the perfection of a well-designed machine? OK, so there are some phenomena that correlate (bear a resemblance to) with how computers behave. well, there are phenomena that correlate with a great many number of things; we shouldn't be surprised that computers and information theory are one of them
krastanov 10y ago
Minor nitpick: We definitely do not know whether everything is discrete. There are plenty of quantum mechanical phenomena that do not have discrete spectra (you can have light of any wavelength for instance (with some caveats at the extremes of the energy scales)). We also do not have theoretical or experimental proof that space-time is discrete at the Plank length-scale - all we know is that our current theories break at that scale. See https://physics.stackexchange.com/questions/9720/does-the-planck-scale-imply-that-spacetime-is-discrete https://physics.stackexchange.com/questions/9720/does-the-pl... (the given answer is pretty great, but beware, the author is known for being a bit hostile in his non-physics opinions)
- eutectic 10y ago
  Luboš is known for being extremely hostile in all his opinions. :)
- aphextron 10y ago

ycmbntrthrwaway 10y ago

> Here is a model of waves, as in light or sound, but not as in water waves or electron waves How water waves are different from sound? Water wave are sound, aren't they?

ajkjk 10y ago
Well, water waves can either be surface waves or pressure waves. The latter is the same mechanism as sound.
btilly 10y ago
The wave that he is modeling is due to having a field in space-time that will interact with nearby values of the same field in a linear way, which results in it moving at a constant rate. The waves that you see in water are the surface representation of 3-d movements under the surface of the water. So you get effects such as the depth of the movement for a wave determines its velocity. A wave that moves a very deep water column moves very fast. (One that is a half-mile deep can move as fast as a jet!) A wave that moves a shallow water column moves slowly. Another interesting fact about waves is that there is a significant nonlinear interaction between the depth of the water and the depth of the wave. As you come to shore this causes the wave to rise up. Surfers enjoy this effect when it comes to normal wind driven waves. But in the case of very deep and fast waves, the effect is very much like a tide unexpectedly coming in. The result is known as a tsunami or tidal wave. These complex behaviors mean that water waves can behave very differently from light and sound.

d_burfoot 10y ago

> Since you are a programmer, you do not know what science is, even though you may believe you do. A hint: Computer science does not contain science, just mathematics. He probably wrote this half in jest, but it is actually a serious issue in fields like Natural Language Processing and Computer Vision that are have their intellectual roots in Computer Science. Papers in CV and NLP are about data structures, algorithms, software engineering methods, neural networks, statistical models, and so on. They do not discuss anything in particular about the structure of language or the properties of images. This is because they are descended from CS. In CS, exemplar results are ideas like QuickSort and Dijkstra's algorithm. These algorithms work on any list or graph; you do not have to know anything special about the particular properties of the list or graph you are operating on. As an illustrative anecdote, I went to an NLP talk given at MIT by a well-known Google/Berkeley parsing researcher. He gave a talk about a system that used neural networks to do sentence parsing. In the QA session, I mentioned the idea of verb argument structure, and asked how the system would learn, for example, that a verb like "persuade" or "argue" can take a that-complement, while other verbs cannot. He didn't really have an answer, because it wasn't the kind of thing that he worried or thought about. My guess is that he did not consider such a question to be relevant to his field.

deleted 10y ago
[deleted]
neshibble 10y ago
I do research on Deep Learning. That seems the exact kind of question they would deem relevant to their field. I don't know much about NLP but if I had to guess the answer to your question is include it in the training data. I don't know what model they use, but presumably it parses out sentence structure in a specific format and uses that as input to some neural network architecture. Not really sure why he didn't answer your question, it's the exact kind of question people do NLP to answer.

Coding_Cat 10y ago

Hey, something I can comment on properly for once ;). Handed in my final Quantum-field-theory homework yesterday (or blood-sweat-and-theory as I called it, great fun) and finishing a MSc. in Computational science 'soon'. From what I can follow, most of it is, unfortunately either varying degrees of wrong or just confusing as all hell. :\ Some assorted quotes: >The electron is not in a single place, but instead spread out over all the positions, more or less. This is called "superposition". No, the superposition principal states that individual states (contributions) can be summed in a linear fashion. I know this is not a very clear way of wording it, but it is one of those things I think is quite hard to word but very easy to understand once you see it. (Although one could say this is a form of superposition, namely a sum of infinite delta functions in position-space. But this would be the most confusing example to use) >The smart programmer would guess at a model containing more complex math that will get the array to model several particles, but no such thing exists. Quantum field theory. > These examples have used cubes with a width of 1000 voxels, and of 1000 time instants. The Universe use a width of something like 10^70 voxels. The same goes for time. I assume this is (roughly matches) size-of-observable-universe/plank-length. But this is misinterpretation of the planck length. As far as we (I) know, spacetime is continouis. (string theorist migth disagree, I am not familiar). Furthermore, the many particle approach is not at all reasonable. One would (usually) use lattice-QFT. where one simulates a field for each type of particle (the field can have several components) and particles are identified as excitation of this field. The most well known is lattice-QCD. >Quantum Electro Dynamics Quantum Electrodynamics ;) >Richard Feynman got the nobel prize for figuring out a way of doing this. His Quantum Electro Dynamics is a sort of dynamic programming method This part is right (I have no idea what the next few sentences are trying to say). Feyman diagrams (those fun squilly drawings) represent the results of some awful, awful integrals. The real analytical answer is integrated over two infinite spaces. But one can do a taylor expansion to get a answer which can be computed. Feynman noted that you can read off a few rules from this approximation and assign drawings to them. The answer can then be computed by summing all (topologically distsinct graphs) instead of the terms in the Taylor sum. It's much easier than it sounds (and sure as hell more fun than doing integrals), and you can copy-paste entire sections of your diagrams as long as the in and out-puts match up. perfctly suitable for dynamic programming.

halfnibble 10y ago

I feel like this is what's wrong with the world: "In science one guesses at explanations. One does not deduce them like one do in math." As a programmer who took quantum mechanics in college, I have to admit, I didn't understand most of it. Someone I respect once told me that if you think you understand quantum mechanics, then you don't understand any of it at all. The mathematical portion, vector mathematics with imaginary numbers, was the only part that was interesting to me. It seemed to me that mathematical deductions were necessary because the phenomenon modeled nothing in our "reality."

madhadron 10y ago

This puzzles me extremely. There are very insightful statements like > One does not deduce them like one do in math. The physicists who actually did this stuff apparently knew this, and considered the math more akin to toying with the models to see what happens, to see if they could get better models Which is absolutely true. Part of the problem with quantum mechanics texts is that they're almost all descended from Oppenheimer's lectures (via Schiff's book) to graduate students who already knew this, and just needed someone to brain dump the latest techniques. But then it's mixed with really basic misunderstandings, like > Many physicists like to believe that this makes the underlying model irrelevant; that the matrix behaviour, its eigenvalues, is the only thing that matter. You will encounter lots of this in books about Quantum Mechanics. This however is not science, because it ignores Ockhams Razor; the models shall be the simplest ones. A sparse matrix is simpler than when it is Fourier transformed, or put into atom orbitals. (I thank Eliezer Yudkowski who gave a reminder that Ockhams razor belongs here too.) Quoting Eliezer Yudkowski is a useful heuristic for not taking someone seriously, but this quote implies that the author missed the whole point of linear algebra. And is falling into the traps described by Theorem IV in van Kampen's [Ten Theorems about Quantum Mechanical Measurements](http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=617AE275E5CECF5F0AFD69ACBC52141B?doi=10.1.1.205.6529&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=617...).

partycoder 10y ago

You can also read the Feynman lectures on computation, has some notes on quantum computing.

B1tchard0 10y ago

This article could have been written by an algorithm. Everyone knows the meme about Quantum Mechanics being incomprehensible, like, ~"if you understand quantum mechanics, you don't understand quantum mechanics". Quantum Mechanics requires randomness, because determinism is scary. Both probability and fate are functions of time, and time is the most interesting thing to look at. Generally, Time is ignored, or at best "accounted for". As a programmer I think time is more interesting than particles or fields or probabilities of wave-function whatever

AgentME 10y ago
>Quantum Mechanics requires randomness, because determinism is scary. Isn't the many-worlds interpretation generally regarded as deterministic?
- n4r9 10y ago
  Yes, as is de-Broglie-Bohm interpretation. Some others make no assertions about determinism. I interpreted "because determinism is scary" as a tongue-in-cheek aside. Either way, time is not ignored: there is serious research effort into the concept of time in quantum mechanics.
- naasking 10y ago
  IIRC, it's deterministic in a sense that isn't equivalent to the way de Broglie-Bohm is deterministic. The latter is generally what people mean by deterministic, ie. it's a classical theory with an extra term to account for quantum influences.
  - n4r9 10y ago
    Both theories model the universe as being in a definite, non-probabilistic state, and that the state at one time determines the state at all future times. But yeah there is some difference in the anthropocentric aspects, i.e. how our observation of probabilities actually arises.

hota_mazi 10y ago

It's puzzling to see the author call himself multiple times a scientist while lending so much importance to Occam's razor (which is spelled differently in the article, not sure if it's an alternative spelling in his language or a mistake). Occam's razor is not a law. It's not a fact. It's a simple suggestion if you're looking for a starting hypothesis. Not sure which way to start to investigate a phenomenon? Pick the simplest one and verify that one. It doesn't mean it's right, it doesn't mean it's wrong, just that it's a reasonable first guess. But not a proof. Not a fact. Just a guess that's statically more likely to be right.

defined 10y ago
Occam is the Latinized version of Ockham, as in "William of Ockham" [1]. [1]: https://en.m.wikipedia.org/wiki/William_of_Ockham https://en.m.wikipedia.org/wiki/William_of_Ockham
- TheOtherHobbes 10y ago
  Which must be the correct spelling, because it's shorter.
- deleted 10y ago
  [deleted]
stan_rogers 10y ago
Ockham is arguably the proper spelling when the name isn't being rendered in Latin; Ockham is where William was from.
dragonwriter 10y ago
> It's a simple suggestion if you're looking for a starting hypothesis. While it can be used to select priority for exploring hypotheses, it's at least as valuable as a method of choosing from among models with equal explanatory power once they've been tested and established to have equal explanatory power.
sideshowb 10y ago
Ock/cham's razor is a heuristic, not a law. It also runs into weirdness combined with MWI. Are infinite universes the simplest explanation, or have you just literally broken Occam's razor in the most egregious way possible?

yorwba 10y ago

There is lots of undefined behavior in the code examples, where x-1 is used as an index although x starts from 0. I guess he didn't want to talk about boundary conditions?

sideshowb 10y ago

A slightly wacky article, but I do think there is lots more scope for explaining quantum physics via programming concepts. I got what little understanding I have of QM by creating a game that simulates it. I even made my own wacky article as well :) https://linkingideasblog.wordpress.com/2016/04/25/learning-quantum-mechanics-the-easy-way/ https://linkingideasblog.wordpress.com/2016/04/25/learning-q...

andrepd 10y ago

This article does not elucidate anything about Quantum Mechanics, is quite confusing, and indeed is plain wrong in several aspects. Very disappointing.